4). that: 1) the substitute of mutant LRRK2 with form of the protein in T- and B-lymphocytes diminishes LPS-mediated inflammation and rescues the SNpc DA neuron loss in the mutant LRRK2 brain; 2) the presence of G2019S or R1441G LRRK2 mutation in lymphocytes Rabbit polyclonal to PCDHB11 alone is sufficient for LPS-induced DA neuron loss in the genotypically brain; and 3) neutralization of peripheral IL-6 overproduction prevents the SNpc DA neuron loss in LPS-treated mutant LRRK2 mice. These results represent a major paradigm shift in our understanding of PD pathogenesis and suggest that immune dysfunction in some forms of familial PD may have primacy over the CNS as the initiating site of the disorder. suggesting an active Qstatin role for bacterial infection in the outcome of the disease23,24. Thus, it is now proposed that the immune component in PD occurs early and changes dynamically with the disease progression, contributing to the Qstatin neuronal loss observed in patients. While the vast majority of PD cases arise from unknown causes, about 10C15% have a clear genetic etiology25. At this time, over 90 loci have been associated with PD26, although only a small number of them, including the gene encoding Leucine Rich Repeat Kinase 2 (LRRK2), account for the majority of familial cases27. LRRK2 is known to express in both innate and adaptive immune cells and its expression is tightly regulated by immune stimulation28C34. It has also been shown that LRRK2 expression is significantly increased in inflamed intestinal tissue biopsied from patients with Crohns disease, indicating that LRRK2 might play a more generalized role in the inflammatory process than previously recognized28. A number of studies have shown that peripheral pro-inflammatory cytokine responses to challenge were altered in mice carrying the LRRK2 mutation35C37 as well as in asymptomatic PD patients carrying a G2019S LRRK2 mutation38; suggesting a role for LRRK2 in peripheral inflammation. Our group has recently shown that mice carrying two most common pathogenic LRRK2 mutations, G2019S or R1441G, develop a significantly higher LPS-induced SNpc DA cell loss. We also found that the exacerbated neuroinflammation and SNpc DA cell loss do not depend on the active participation of the brain resident microglia or infiltrating T-cells and/or monocytes, but are likely mediated by circulating inflammatory molecules that are dysregulated by mutant LRRK237. Based on these studies, we now propose that the neurodegenerative cascades in PD emanate from signals arising from the peripheral immune system and that LRRK2-PD is primarily an immune disorder, with secondary effects manifested in the CNS. Since the majority of PD studies focus on the events within the CNS and the contribution of peripheral immune compartments is largely ignored, in this study we have asked a fundamental question: is altered peripheral immune response alone sufficient to initiate neuronal loss in LRRK2-PD? To test this hypothesis, we generated chimeric mice with a adaptive immune system and a LRRK2 mutant brain (and vice versa) and then examined whether this in vivo switching impacts both peripheral and CNS inflammatory response and SNpc Qstatin DA cell loss following exposure to LPS. Herein, we report that the replacement of mutant LRRK2 with LRRK2 in peripheral T- and B-cells diminishes the peripheral inflammatory response to LPS and rescues SNpc DA neuron loss that is observed in fully mutant LRRK2 mice. Additionally, reversed chimera mice carrying normal LRRK2 in the brain but mutant LRRK2 (R1441G or G2019S) in the adaptive immune cells do manifest the LPS-induced SNpc DA neuron loss identical to LPS-treated fully mutant LRRK2 mice. Furthermore, we identified peripheral IL-6 as a key component of inflammation-mediated neuronal loss since neutralization of LPS-induced IL-6 overproduction in R1441G LRRK2 mutants completely abolishes the SNpc DA cell loss. Based on these data we suggest that LRRK2-induced immune dysfunction in PD is not simply a manifestation of the pathology, but primarily drives the development of the disorder, and propose the provocative hypothesis that LRRK2-PD has its etiologies in a malfunction of the adaptive immune response. Results Generation of BM chimeras and characterization of immune phenotype Given that irradiation severely damages both innate and adaptive immune systems as well as the CNS39C43, we first decided to verify whether efficient donor cells engraftment can be achieved in homozygous immunodeficient Rag1?/? recipients without a pre-conditioning regimen (Supplementary Fig. 1a). Rag1?/? mice lack mature T- and B-lymphocytes as a result of the deficit in V(D)J recombination44. In contrast to SCID mice, which develop some functional lymphocytes with age, the phenotype of Rag1?/? mice is described.